1. Field of the Invention
The present invention is directed to an arrangement for an ink-jet printer head that is composed of a number of stacked ink-jet printer modules the modules operating according to the edge-shooter principle and being equipped with plate-shaped piezoelectric actuators.
2. Description of the Prior Art
Ink-jet printer heads of the above type are employed in small, fast printers that are in turn a component of modern machines for franking postal matter or for printing addresses. Such a printer is also suitable as a product labeling means.
Differing from a standard office printer having line-by-line printing, the printing by such heads ensues as a one-time imprint, such as a Franking imprint in one pass of the item to be imprinted, such as postal matter. Corresponding to this significantly larger printing width--approximately one inch--, the number of ink nozzles to be arranged under one another, and thus the number of piezoactuators, in an ink-jet printer head of this type is substantially larger than is the case in ink-jet printer heads for office printers.
In order to satisfy modern requirements--imprints having word and image characters--for postage meter machines with good printing quality, printer resolutions of approximately 200 dpi (drops per inch) are required, which means ink-jet printer heads having the same number of nozzles and piezoactuators given a printing width of one inch.
If all nozzles were arranged in a single nozzle row, the spacing between two neighboring nozzles would be the print density dimension t. Given more than one ink-jet printer module, the print density dimension is derived from the quotient of the nozzle spacing of a module and the number of modules. Standard nozzle apertures lie between 40-50 .mu.m in width. Given an imprint width of one inch and a resolution of 200 dpi, the adjustment errors must be kept below 10 .mu.m.
Necessarily, such ink-jet printer heads are implemented in planar or stacked fashion, first for reasons of allowable dimensions and the packing density that can thus be achieved and, second, for reasons of an economical manufacture, as discussed in German 42 25 799. Surface resonators are usually utilized as piezoactuators, formed by a piezoelectric material, for example lead-zirconate-titanate (PZT), arranged between two metal electrodes. The carrier plate--which simultaneously serves as the membrane plate over the ink printer chambers--can be composed of glass, ceramic, plastic or metal for the piezoactuators.
The way the modules are arranged relative to one another in order to achieve a printing density of 200 dpi and the contacting of the piezoactuators are thus critical problems.
The aforementioned German OS 42 25 799 discloses an ink-jet printer head of the type initially described that is composed of a number of different modules, of which only a nozzle lying at the exterior carries a common nozzle row at its end face. All modules have ink printer chambers desirable by piezoactuators for ink ejection, these chamber being connected via respective channels to the allocated nozzles. The connecting channels from module to module necessarily proceed orthogonally relative to the printer chambers.
Spacer parts are arranged between the modules and have an ink delivery opening and ink passage openings as well as a recess for the piezoactuators. The spacer parts can be one part or two pieces and are composed of the same material as the piezoactuators.
Although the advantage of only a single nozzle row is significant, the technological outlay for manufacturing modules which differ from one another is still substantial.
Higher machines or molding precision is required for the connecting channels which proceed through a number of modules than is required for the ink printer chambers, and a more complicated adjustment procedure is also required. The connecting channels are of various lengths and thus require additional electronic control measures in order to equalize flow and pressure therein.
A piezoelectric ink-jet printer head having a monolithic piezoceramic body is also disclosed in German OS 38 05 279 having transducers arranged parallel side-by-side, each transducer including a planar, piezoelectric drive element, a pressure chamber, and ink channel and a nozzle. The pressure chambers, the ink channels and the nozzles are fashioned as cavities in the piezoceramic body. Each drive element has an outer electrode, an inner electrode and an active piezoceramic layer arranged between the electrodes. The drive elements are piezoelectrically separated from one another by incisions in the active piezoceramic layer. The inner electrodes of the transducers are electrically connected to one another. The electrical connection of the outer and the inner electrodes ensues via a terminal ribbon or, a ribbon conductor. One terminal goes to the inner electrodes connected to one another. The outer electrodes are separately contacted with terminals. The underside of the piezoceramic body and a side thereof lying opposite the nozzle front are secured on a retainer frame. An ink nozzle and the terminal ribbon are conducted through openings in the retainer frame. The nozzle row is inclined relative to the moving direction of the recording medium by means of a slanting integration of the retaining frame in a housing and consequently the print density of the ink-jet printer head is enhanced; also see United Kingdom application 2 264 086, FIG. 3, with respect thereto. A number of retainer frames or ink-jet printer heads can also be stacked above one another and introduced in common into a housing. If one desired to try to stagger the nozzle rows relative to one another, either the retainer frame would have to be differently adapted or the housing would have to have corresponding graduations. The technological outlay, including adjustment outlay, would thereby be substantial.
Lastly, U.S. Pat. No. 4,703,333 discloses an ink-jet printer head wherein a number of ink-jet printer modules operating according to the side-shooter principle are stacked inclined behind one another such that the nozzle region as well as the ink supply region are free. A receptacle frame having slanting steps is matched to this fish scale-like arrangement. In order to achieve the lateral offset of the nozzles relative to one another, the ink-jet printer modules are provided with oblong holes through which screws that engage into threaded holes of the steps are conducted. The modules must be adjusted with a template and then locked with the screws. The individual ink-jet printer module is composed of a nozzle plate, an ink channel plate, a pressure chamber plate, a membrane plate with piezoactuators and a cover plate having a recess for a ribbon conductor for contacting the piezoactuators. An ink delivery channel having two ink connection sockets is machined into the cover plate.
As may be seen from this known disclosure, the number of individual parts and the adjustment outlay are substantial. A cleaning and tightening station adapted to this ink-jet printer head has an extremely complicated structure due to the graduation.